Method of preparing films containing liquid crystalline polymers

ABSTRACT

A method of preparing a film includes the steps of mixing a thermotropic liquid crystalline polymer with a host polymer to provide a first material, coextruding the first material with a second material so as to form a film comprising the first and second materials, quenching the film, and orienting the quenched film in at least one direction. The oriented film has an exposed first major surface that includes protrusions resulting from regions of the liquid crystalline polymer in the host polymer.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a continuation of patent application Ser. No. 07/595,978, filedOct. 11, 1990, now U.S. Pat. No. 5,124,184, which is a continuationapplication of Ser. No. 088,160 filed Aug. 21, 1987, now U.S. Pat. No.4,963,402.

TECHNICAL FIELD

The present invention concerns films having tailorable surface roughnessand, optionally a low coefficient of friction. More particularly itconcerns films which achieve these results without the use of known slipagents.

BACKGROUND ART

Films having tailorable surface roughness and/or a low coefficient offriction have been long sought. Such films are useful in a wide varietyof applications including packaging, printing, electrical insulation,capacitor manufacture, backings for adhesive tapes, magnetic recordingtapes and discs, computer tapes, writeable surfaces, and the like.

The low coefficient of friction is desirable so as to improve handlingproperties of the film during manufacture and use and to preventblocking during storage. The tailorable surface roughness is desirableso as to provide appropriate surface structure to the film. Forinstance, substrates employed in magnetic recording media must berelatively smooth on the surface to which the magnetic coating isapplied. On the other hand, the running or opposite side of the magneticsubstrate, must have a characteristic that resists abrasion fromcontacting surfaces such as tape drive mechanisms. Capacitor films andwriteable films also must have a high surface roughness to respectivelyallow oil impregnation and to accept ink or pencil, etc.

Several approaches have been employed in order to provide a film withsurface roughness and a low coefficient of friction. Generally theyinvolved the use of the so called slip agents (e.g., inorganicparticulates and organic materials which do not dissolve in the hostpolymer), low coefficient of friction coatings, surface texturing andthe like.

Each of these approaches suffers from one or more disadvantages. Forexample, the inorganic particulate slip agents (e.g., silica, talc,mica, glass, calcium carbonate, titanium dioxide, etc.) and thepreviously used non-soluble organic material slip agents (e.g.,crosslinked polymers, combinations of fluorocarbon polymers with fattyacid amides, polycarbonates, polyolefins, etc.) may clog the filtrationdevices used in the manufacture of the film. Additionally, such slipagents may be present as undesirably large agglomerates in the filmwhich negatively effect certain applications such as magnetic recordingmedia.

The use of these slip agents suffers from other disadvantages. Theincorporation of inorganic particulates usually requires that they bemilled to the appropriate size. This is an added step that is difficultto control, provides particles of widely varying size, (resulting inunpredictable surface roughness in the film), and adds cost. The use ofthe non-soluble organic materials usually requires a large loading andmakes recycling the film difficult.

The application of low coefficient of friction coatings (e.g., siliconecoatings) to the surface of the film also suffers from variousdisadvantages. For example, such coatings generally are not durable, theapplication of such coatings complicates the manufacturing process andadds cost, and many of such coatings detrimentally affect the adhesionof the film to subsequently applied materials.

Surface texturing of the film is usually achieved by external means suchas treatment of the surface with sputter etching, and the like. Suchtechniques also complicate the manufacturing process and add cost.

A film has now been discovered which overcomes these disadvantages ofthe prior art. The film not only possesses the unique characteristicthat its surface roughness can be tailored to suit the users needs, italso preferably has a low coefficient of friction. Furthermore,manufacture of the film does not quickly clog the filtration devicesused during such manufacture thus extending the useful life. Theseresults are achieved by incorporating a thermotropic liquid crystallinepolymer (sometimes referred to hereinafter as LCP) with a host polymer.

The use of LCP's with other polymeric materials has been previouslysuggested. See, for example, U.S. Pat. No. 4,442,057 in which acombination of a fiber-forming polymer and a small amount of a polymercapable of forming an anisotropic melt (an LCP) is melt spun at aminimum windup speed of 1,000 meters per minute. This patent is directedsolely to the proposition that the LCP provides windup speed suppression(i.e., the properties of the spun fiber are those that would be obtainedfrom a fiber spun at a lower windup speed).

Other patents which disclose the use of LCP's with other polymericmaterials include United Kingdom Patent No. 2,078,240 which disclosesthe use of from 25 to 95 percent by weight LCP with the other polymer;U.S. Pat. No. 4,408,022 which discloses the use of from 25 to 50 percentby weight LCP with one or more additional polymers; U.S. Pat. No.4,451,611 which discloses the use of from 85 to 95 percent by weightLCP; and EPO Patent No. 169,947 which discloses the use of from 20 to 80percent by weight LCP in combination with another polymer. These patentsare each directed to blends of polymers useful as injection moldingresins. Although some also state that the blends can be used in theformation of fibers and films, nothing is stated with respect to theformation of low coefficient of friction films having a tailorablesurface roughness, oriented films of this type, or the formation ofdiscrete regions of the LCP in a matrix of the host polymer.

Still other publications which disclose the use of LCP with anotherpolymer are EPO Patent Application 0 071 968 which discloses athermoplastic composition containing an isotropic thermoplastic materialand an oligomeric thermotropic (liquid crystalline in the meltadditive); and Japanese Kokai JP 61-78862 and JP 61-78863 which disclosea biaxially oriented film respectively containing 1-60 weight percentand 1-15 weight percent liquid crystalline material in a matrix polymer.The EPO publication is silent with respect to the formation of discreteregions of the LCP and the host polymer. Additionally, none of thesepublications disclose low coefficient of friction properties or a filmhaving a tailored surface roughness.

Moreover, films disclosed in the two Japanese publications are said topossess improved bulk properties, such as improved elastic modulus,impact resistance, and dimensional stability, due to the formation ofacicular (i.e., needle-like or rod-like regions) of the LCP inpolyester. The LCP regions have a high aspect ratio which results fromemploying a draft ratio (i.e., degree of melt stretching) of 3-30 timesin the film manufacture.

DISCLOSURE OF THE INVENTION

The present invention is directed to a novel film which contains athermotropic liquid crystalline polymer and a host polymer. The filmfurther comprises a rough surface which has a plurality of protrusionsor projections. In its preferred sense, the film has a low coefficientof friction. These results are achieved without the use of conventionalor known slip agents, added surface coatings, or surface texturingprocesses.

As used herein, the phrase "coefficient of friction" includes both thecoefficient of static and the coefficient of kinetic friction. Thesecoefficients are measured according to the procedures identified in ASTMD-1894-78. Although each coefficient identifies a differentcharacteristic of the film, each is low in the present invention. Thefilm preferably has a coefficient of friction of less than about 0.8,more preferably one of less than about 0.4. Surprisingly the surfaceroughness of this film can be increased without negatively affecting itscoefficient of friction.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a photomicrograph of the surface of a film of the invention;and

FIG. 2 is a graphic presentation of the pressure drop across a 5 micronfilter as a function of cumulative throughput.

DETAILED DESCRIPTION

The present invention is directed to a film, i.e., a structure, whosethickness is substantially less than either its length or width andwhich has two, essentially parallel opposed surfaces. As used herein,the term "film" includes sheets, ribbons, tapes, discs, and the like.

FIG. 1 is a 400X photomicrograph of the surface of the film of theinvention. This film, which contained 0.24% LCP in poly(ethyleneterephthalate), was 37 microns thick. As can be seen, the surfacecomprises a plurality of individual protrusions of varying height andshape. The protrusions are randomly distributed over the surface and arethe result of the presence of identifiable regions of the LCP in thefilm.At lower concentrations of LCP (e.g., 25 percent by weight or less)the surface of the film substantially comprises the host polymer and theLCP regions may be said to be dispersed in the host polymer. At theseconcentrations the LCP regions are generally covered by a thin layer ofthe host polymer although such regions may occasionally be exposed. Athigh concentrations of LCP (e.g., above about 25 weight percent) more ofthe regions are exposed on the surface. The number of regions which areexposed continues to increase until above about 50 percent by weight theLCP regions comprise the predominant material of the surface. At theseconcentrations, the host polymer may be said to be dispersed in the LCPregions.

The LCP regions are three dimensional structures which may becharacterizedas generally globular. As such they may be symmetrical(e.g., spherical, elliptical, etc.) or asymmetrical in cross-section.Usually they are asymmetrical and have a low aspect ratio. As a resultthe majority of LCP regions are neither acicular nor rod like. The LCPregions are typically readily discernable under an optical microscopeusing crossed polarizers. Usually they are from 0.2 to 20 microns indiameter or major axis and cause protrusions of at least 1 nanometer(preferably at least 5 nanometers) from the surface (as described morefully hereinafter. Although both smaller and larger regions may providea useful film, the efficiency of the LCP drops when the regions areoutside of this range.

The quantity of LCP employed in the invention may vary over a ratherwide range. Thus, as little as 0.01 percent by weight LCP may be used.Surprisingly, varying the quantity of LCP employed varies the surfaceroughness of the film. For example, the LCP preferably comprises from0.04to 80 percent by weight of the film. More preferably the LCPcomprises from0.04 to 3 weight percent LCP (most preferably from 0.04 to1 weight percent) when smoother films are desired (e.g., RQ values ofless than 80 nanometers). If a film having a rougher surface is desired,the LCP typically comprises more than 1 weight percent of the film.

The values for surface roughness reported herein refer to the root meansquare average peak height (RQ). Techniques for determining the RQ valueare set forth hereinafter. Higher RQ values indicate rougher surfaces.

The ability to tailor the surface of the film of the invention to adesiredroughness permits one to design specific films for specificapplications using the same ingredients. For example, magnetic recordingmedia such as video tapes, audio tapes, floppy discs, computer tapes andthe like, require a smooth surface for application of the magneticrecording material. These devices can be prepared by applying either alayer of magnetic recording media in a binder or a free metal layer to afilm of the invention comprising from 0.04 to 0.5 weight percent LCP.This provides a film having a maximum surface roughness of about 60nanometers.Smoother surfaces (surface roughness of less than 25nanometers) can be provided by employing from 0.04 to 0.2 weight percentLCP.

Capacitor films, on the other hand, require a very rough surface (e.g.,RQ of 200 nanometers or more). These films should comprise at least 2weight percent LCP.

If a printable surface is desired, a surface roughness (e.g., RQ) of 100nanometers is required. At least 1 weight percent LCP should be used.

If a writeable (e.g., with pen or pencil) surface is desired, an evenrougher surface (e.g., RQ of 500 nanometers or more) is needed. In thiscase the level of LCP utilized in the film should be greater than 3weightpercent.

As previously noted, the film preferably possesses a low coefficient offriction. Surprisingly, the low coefficient of friction is achieved atvery low levels of LCP (e.g., 0.04 percent by weight). Even moresurprisingly, the quantity of LCP employed can be varied as describedabove without significantly affecting the coefficient of friction. Forexample, at LCP concentrations of 0.04 to 3 weight percent thecoefficientof friction is less than 0.8 (preferably from 0.2 to 0.5).The coefficient stays within this range even at levels above 3 weightpercent.

The precise nature of the relationship between the LCP and the hostpolymerin the invention is not fully understood. Thus, the LCP mayinteract with the host polymer in some manner such as by beingphysically intertwined with the host polymer or by being partiallyreacted with it in the form ofa transesterified blend of the LCP and thehost polymer. However, it is important that the regions of LCP and hostpolymer remain identifiable in any partially reacted product, as it hasbeen found that if the LCP is entirely reacted with the host polymer theresultant film loses its ability to provide reduced coefficient offriction and a controlled surface roughness.

The thermotropic liquid crystalline polymers useful in the presentinvention are either capable of forming an optically anisotropic meltwhenheated to a particular temperature range or can be induced to formsuch a melt by the application of shear to the polymer. Generallyspeaking, any thermotropic liquid crystalline polymer, can be used inthe invention. It has been found that LCP's having melting temperaturesless than, equal to,or greater than that of the host polymer can besuccessfully employed in the invention. However, if the meltingtemperature is less than that of the host polymer, it has also beenfound that a higher concentration of LCP is required to achieve a givenresult. The melting temperature of the LCP must be less than thedecomposition temperature of the host polymer.

The chemical structure of the LCP has been found to have some influenceon the coefficient of friction and surface roughness of the film. Ingeneral,if the LCP has a chemical moiety similar to that of the hostpolymer, or ifthe LCP is thermodynamically miscible with the hostpolymer, the coefficient of friction will be higher and the surfaceroughness will be lower.

Preferably the LCP is a wholly aromatic polyester or polyesteramide.Such materials comprise two or more recurring moieties which, whencombined, form an optically anisotropic melt phase. Wholly aromaticpolyesters are materials in which each moiety present in the polyestercontributes at least one aromatic ring to the polymer backbone and inwhich each moiety contains little, if any, non-aromatic constituents inthe backbone. It is preferred that the wholly aromatic polyester containvirtually no non-aromatic constituents in the backbone. Although the LCPmay contain non-aromatic constituents in the backbone, it has been foundthat such constituents reduce the effectiveness of the LCP. Suchpolyesters are known. For example, 4-hydroxybenzoic acid copolymers and6-hydroxy-2-naphthoic acid copolymers can be employed as the LCP.

Wholly aromatic polyesters are disclosed in a number of printedpublications. See, for example, U.S. Pat. Nos. 4,067,852; 4,083,829;4,130,545; 4,161,470; 4,184,996; 4,219,461; 4,224,433; 4,130,817;4,238,598; 4,238,599; 4,245,084; 4,256,624; 4,265,802; and 4,279,803.

Generally speaking the above-mentioned LCP's are formed by a variety ofester-forming techniques in which organic monomer compounds whichpossess functional moieties are reacted. For example, the functionalgroup of the organic monomers may be carboxylic acid groups, hydroxylgroups, ester groups, acyloxy groups, acid halides, etc. The monomersmay be reacted viaa melt acidolysis procedure. Typically the monomersare heated to form a melt from which volatiles evolve. Vacuum is usuallyapplied at a later stage to facilitate removal of the volatiles formedduring the condensation reaction.

Examples of LCP materials useful in the present invention include"Vectra" A900 available from Hoechst Celanese Corporation (believed tobe a copolymer of 4-hydroxy benzoic acid and 6-hydroxy naphthoic acid):LCC 10108 (a copolyester of 60 mole % oxybenzoate and 40 mole % ethyleneterephthalate) and LCC 10109 (a copolyester of 80 mole % oxybenzoate and20 mole % ethylene terephthalate) both available from Eastman ChemicalsDivision of Eastman Kodak Company. Other LCP materials useful in theinvention include "Xydar" LCP available from Dartco (a copolyester ofp-oxybenzoate, p,p'-biphenol, and terephthalate), and the copolyesterssuch as those disclosed in U.S. Pat. No. 4,377,681 includingcopolyesters of p-oxybenzoate and hydroquinone with either an aliphaticdicarboxylate or 2,2-bis(4-hydroxyphenyl) propane and isophthalate.

The host polymers useful in the invention are those materials which arecapable of being extruded or cast and solidified to form a dried,preferably self-supporting film. They may be selected from a variety ofmaterials including, by way of example, polyesters (including aromaticpolyesters), polyamides, polyimides, polycarbonates, polyolefins,acrylic polymers, vinyl chloride and vinylidene chloride and fluoridebased polymers, polystyrene, polyphenylene oxide polymers, polysulfonesand polyether sulfones, polyketones and polyether ketones,polyoxymethylenes, thermoplastic cellulosic polymers and the like. Thesematerials may be used individually, as mixtures of two or more polymers,and as copolymers.

A particularly useful class of host polymers is the polyalkyleneterephthalates and their copolyesters. These polymers, many of which areavailable commercially, can be prepared by known techniques such as bythealcoholysis of esters of terephthalic acid with alkylene glycols andsubsequent polymerization, or by heating the glycols with the free acidsor with halide derivatives thereof with subsequent polymerization, andsimilar processes.

The alkylene units of the polyalkylene terephthalates generally containfrom two to ten (preferably from two to four) carbon atoms. Mostpreferably they contain two carbon atoms. Specific examples of usefulpolyalkylene terephthalates include poly(ethylene terephthalate),poly(butylene terephthalate), poly(isobutylene terephthalate),poly(pentylterephthalate), poly(isopentyl terephthalate), andpoly(neopentyl terephthalate). The alkylene units may be straight orbranched chain units.

Other specific examples of useful host polymers includepolyhexamethylene adipamide, polycarbonate, polyethylene, polypropylene,polyvinyl chloride,polyvinylidene chloride, polyphenylene sulfide,polyvinylidene fluoride, polyvinylfluoride, polymethylmethacrylate, andthe like.

A variety of other ingredients may be incorporated into the films of theinvention. For example, conventional slip agents may be utilized ifdesired, although their incorporation is not necessary. Ultravioletlight absorbers, antioxidants, colorants and the like may alsoincorporated if desired. Generally these other ingredients comprise lessthan 5 weight percent of the film.

The film of the invention may comprise either a single layer film of theLCP and the host polymer, or a multilayer structure in which theLCP/host combination make up one of the layers. When the film isprovided as a multilayer structure, the LCP containing layer generallycomprises one of the exposed surfaces of the film.

The films of the invention may be readily prepared by a number oftechniques. For example, the individual components may be provided inthe form of particles or pellets, the appropriate amount of eachmeasured out and added to a mixing vessel, and then the ingredientsmixed at ambient conditions so as to produce a substantially uniform dryblend of the components. This blend may then be charged to a suitablemixing vessel, such as a single screw extruder equipped with suitablemixing elements (e.g., a mixing screw or a static mixer), of appropriatelength, or to a twin screw extruder equipped with suitable mixingelements. The blend should be melted at a temperature above the meltingtemperature of the LCPand the host polymer and mixed intimately todisperse the LCP in the host polymer and provide identifiable regions ofthe liquid crystalline polymerin the host polymer. The extruder may alsobe equipped with a filter (e.g.,1 to 200 micron pore size) to helpdisperse the LCP and remove undesirable foreign matter and gels.

After being mixed as described above, the now dispersed blend of LCP andhost polymer may be extruded with an extruder through a filter (e.g., 1to200 micron size) and a die of appropriate shape and cast onto aquenched orchilled roll to form an amorphous case web. Surprisingly, themolten mixture of LCP and host polymer does not plug the filter. As aresult, filter life is extended and product quality is enhanced.

The web may then be oriented by stretching in the lengthwise direction,forexample at a temperature of from 80° to 95° C. and then in the crossdirection at a temperature of from 190° to 210° C.followed by beingheatset at a temperature of from 200° to 250° C. (when poly(ethyleneterephthalate) is the host). The exact temperatures used depend on themajor component of the film and are known to those skilled in the art.If desired, lengthwise and cross orientation may be achievedsimultaneously. Typically the webs are stretched to from one to fivetimes their original dimension during orientation. As such, the lengthto width stretch ratio may vary from 1:1 to 1:5 and from 5:1 to1:1. Thenow oriented film may be wound up and stored for later processing or maybe further processed with no intermediate storage.

Other techniques may be used to prepare the combination of the LCP andhostpolymer. For example, a master batch of the LCP at a concentrationhigher than that ultimately desired may be prepared with the hostpolymer. This master batch may then be combined with additional hostpolymer to provide the desired LCP concentration. Generally, the levelof LCP employed in themaster batch process is from 3 to 15 times greaterthan the final desired LCP concentration.

Additionally, in either of the previously mentioned techniques, severalmanufacturing variations are possible. For example, the LCP may beintroduced into the polymerization mixture for the host polymer at thebeginning, middle, or end of the polymerization process. The LCP is thenmixed with agitation during the process so as to uniformly disperse itthroughout the host polymer. If the mixing is adequate, it is morepreferable to introduce the LCP into the polymerization mixture at theendof the polymerization process so as to minimize the chemical reactionbetween the LCP and the host material.

Whatever the master batch technique utilized, the molten master batchmay be fed directly to a suitable mixing vessel and combined withadditional host polymer to form the film or, alternatively, it may besolidified and subsequently ground or pelletized for latter use.Preferably the particlesof the master batch blend have a size roughlyequivalent to the particle size of the additional host material withwhich it is to be mixed.

The present invention is useful in a variety of ways. For example, itmay serve as a substrate for magnetic recording media (e.g., particulatemagnetic materials in a binder and metallized magnetic tape), abrasivemedia (e.g., particulate abrasive materials in a binder), reinforcingpolymer backings, radiation sensitive compositions (e.g., diazo systems,photoreactive polymers, etc.), adhesives, and the like. It may also beused to provide writable and/or printable surfaces, capacitor films,etc.

The present invention will be further explained with reference to thefollowing examples wherein all percentages are percentages by weightunless specified otherwise. These examples are intended to furtherillustrate the present invention without limiting it.

EXAMPLES 1-11

A series of films were prepared from two thermotropic liquid crystallinepolymers and poly(ethylene terephthalate) (hereinafter PET). Masterbatches of the LCP and the poly(ethylene terephthalate) were prepared.TheLCP, which comprised from 2% to 5% by weight of the batch, was dryblended with the PET at ambient temperature, dried at 149° C. and thencharged to a single screw extruder. The blend was mixed at a temperatureof between 260° and 280° C., extruded through a static mixerin the neckof the extruder, and passed through a 60 micron filter. The extrudatewas solidified by passing it through a water bath and then pelletized.The pelletized master batch was dried at 149° C. and then charged usingan Acrison feeder to an extruder together with additional PET, mixed ata temperature of between 260° and 290° C. and then extruded through adrop die onto a chilled roll maintained at a temperature between 65° and66° C. A draft ratio (degree of melt stretching) of 1.5 was utilized. A30 micron filterwas used to insure that foreign matter and largeagglomerations of unmeltedpolymer were not present in the film. Thequenched films were then stretched to 3.2 times their originaldimensions in both the length and width directions and heatset at 204°C. The resulting biaxially oriented films were then tested forcoefficient of static and kinetic friction using ASTMD 1894-78. Thesurface roughness was determined using the technique set forth inJournal of the Institution of Electronic and Radio Engineers, Vol. 55,No. 4, pp. 145-150, April, 1985 for roughnesses of less than 200nanometers. For roughnesses of more than 200 nanometers, roughness wasdetermined using the technique set forth in Hamilton, D. K. and Wilson,T., 1982, "Surface Profile Measurement Using the Confocal Microscope",Applied Physics, Vol 53, No. 7, p. 5320. In either case, RQ isdetermined from the formula ##EQU1##where RQ=the root mean squareaverage peak height

n=the number of data points

z_(i) =height of the ith point

z=the linear regression value of the surface heights over the entiredata collection area of n data points.

The compositions made and the results achieved are set forth in Table 1.

                                      TABLE 1                                     __________________________________________________________________________                  EXAMPLES                                                        INGREDIENTS   1   2  3  4  5  6  7  8  9  10 11                               __________________________________________________________________________    Poly(ethylene 100 99.96                                                                            99 99.9                                                                             99.77                                                                            99.88                                                                            98.08                                                                            97.33                                                                            99.76                                                                            99.4                                                                             99                               Terephthalate)                                                                (%)                                                                           Vectra A900.sup.(1)                                                                         --  0.04                                                                             0.04                                                                             0.09                                                                             0.09                                                                             0.12                                                                             0.12                                                                             0.17                                                                             0.24                                                                             0.6                                                                              1                                (%)                                                                           LCC 10108.sup.(2)                                                                           --  -- 0.06                                                                             -- 0.14                                                                             -- 1.8                                                                              2.5                                                                              -- -- --                               (%)                                                                           RESULTS                                                                       Coefficient of Friction                                                       (static)      >5  0.75                                                                             1.1                                                                              0.3                                                                              0.3                                                                              0.31                                                                             0.3                                                                              0.28                                                                             0.26                                                                             0.25                                                                             0.27                             (kinetic)     >5  0.34                                                                             0.75                                                                             0.32                                                                             0.33                                                                             0.33                                                                             0.33                                                                             0.29                                                                             0.3                                                                              0.28                                                                             0.29                             Root Mean Square Average                                                      Peak Height (Nanometers)                                                      Air Side         4.9                                                                            13 9.7                                                                              17.5                                                                             13.3                                                                             17.3                                                                             23.3                                                                             22.2                                                                             26.9                                                                             46 68                               Roll Side        6.5                                                                            7.5                                                                              4.3                                                                              18 8  20.3                                                                             18.6                                                                             23.6                                                                             31.5                                                                             55 74                               __________________________________________________________________________     .sup.(1) Believed to be a copolymer of 4hydroxy benzoic acid and              6hydroxy-2-naphthoic acid, available from Hoechst Celanese Corporation.       .sup.(2) A copolymer of ethylene terephthalate and 4hydroxy benzoic acid,     available from Eastman Chemicals Division, Eastman Kodak Company.        

The surface of the film of Example 1 had some undulating ridges (ratherthen discrete peaks or protrusions) which provided some roughness to thefilm. However, as can be seen, this film has extremely high coefficientsof friction. The films of the invention, on the other hand, had atailoredsurface and low coefficients of friction. Furthermore, theirsurfaces comprised discrete protrusions or peaks resulting from thepresence of discrete globules of LCP in the film. The surface of thefilms further essentially comprised poly(ethylene terephthalate).

EXAMPLE 12

A series of films were made using the techniques described above exceptthat a 5 micron filter was employed in place of the 30 micron filter.The pressure drop across the 5 micron filter was determined as afunction of cumulative throughput. The results are shown in FIG. 2.

In FIG. 2, Curves 10 and 12 represent PET films having no slip agent;

Curve 14 represents a film of PET and 0.3 weight % SiO₂ ;

Curve 16 represents a film of PET and 0.2 weight % CaCO₃ ;

Curve 18 represents a film of PET and 0.1 weight % Vectra A900 LCP fromCelanese;

Curve 20 represents a film of PET and 0.2 weight % Vectra A900 LCP fromCelanese; and

Curve 22 represents a film of PET and 0.5 weight % LCC 10108 LCP fromEastman.

As can be seen, PET with no slip agent (Curves 10 and 12) filters well.However, this film is difficult to handle and blocks (sticks to itself)because of the absence of slip agent. The films made with the inorganicslip agents (Curves 16 and 18) initially show good filterability.However,as the cumulative throughput increases, the pressure drop acrossthe filterincreases dramatically indicating that the filter is beingplugged. The films of the invention (Curves 18, 20 and 22) showfilterability comparable to that of PET with no slip agent. However, theresultant filmsdo not have the handling problems of films with no slipagent.

EXAMPLES 13-16

A master batch of LCP (Vectra A900 from Hoechst Celanese Corporation) inpolycarbonate (Merlon from Mobay Chemical Company) at a weightconcentration of 1% was made by dry blending, followed by extrusionthrough a static mixer and a 40 micron filter, followed by pelletizing.After proper drying, the master hatched pellets were dry blended withmorepolycarbonate and fed to an extruder at 292° C. to make cast webswith final concentrations of 0.2, 0.3 and 0.5 % LCP. The cast webs werethen stretched at 175° C. 1.75×1.75 times biaxially into films. Thecoefficients of friction (COF) of the resulting films were:

                  TABLE 2                                                         ______________________________________                                        Example  LCP (%)     Static COF                                                                              Kinetic COF                                    ______________________________________                                        13       0           3.3       4.0                                            14       0.2         0.45      0.57                                           15       0.3         0.48      0.49                                           16       0.5         0.32      0.42                                           ______________________________________                                    

All the films containing LCP had good COF's and slip property ascompared with example 13 which did not have LCP in it. The surfaces ofthe films ofExamples 14-16 comprised a series of discrete projectionscreated by discrete globules of the LCP in the film. The surfacesfurther comprised polycarbonate.

EXAMPLES 17-20

A series of films of the invention were made. A master batch of LCP(VectraA900 from Hoechst Celanese Corporation) in PET at an LCP weightconcentration of 1% and a master batch of another LCP (LCC 10108 fromEastman Kodak Company) in PET at a LCP weight concentration of 5% wereeach made by dry blending, followed by extrusion through a static mixerand a 60 micron filter, followed by pelletizing. After proper drying,the master-hatched pellets were then dry blended with more PET and fedto an extruder with a 5 micron filter to make cast webs with finalconcentrations shown in the table below. The cast webs were thenstretchedat 99° C. 4×4 times biaxially and heatset at 237° C. intofilms. The coefficients of friction (COF), and the RQ were thendetermined. The results are shown in Table 3 below.

                  TABLE 3                                                         ______________________________________                                                LCP                         RQ                                                Vectra/LCC  Static   Kinetic                                                                              Wheelside                                 Example (%)         COF      COF    (nm)                                      ______________________________________                                        17      0.04/1      0.47     0.43   10.5                                      18      0.07/1      0.36     0.37   --                                        19      0.1/1       0.34     0.36   14.4                                      20      0.2/1       0.24     0.33   19.7                                      ______________________________________                                    

EXAMPLES 21-24

A series of films according to the invention were prepared. A masterbatch of LCP (Vectra A900 from Hoechst Celanese Corporation) in PET at aweight concentration of 1% was made by dry blending, followed byextrusion with astatic mixture and a 60 micron filter, followed bypelletizing. After proper drying, the master-hatched pellets were thenmixed with more PET and fed to an extruder with a 5 micron filter tomake cast webs with finalconcentrations of 0.04, 0.07, and 0.09% percentLCP. The cast webs were then stretched at 99° C. 4×4 times biaxially andheatset at 237° C. into films. The coefficients of friction (COF) and RQof the resulting films were then determined and are reported in Table 4.

                  TABLE 4                                                         ______________________________________                                                                          RQ                                                    LCP    Static     Kinetic                                                                             Wheelside                                   Example   (%)    COF        COF   (nm)                                        ______________________________________                                        21        0      >5         >5     1.1                                        22        0.04   0.38       0.37  14.8                                        23        0.07   0.64       0.42  15.5                                        24        0.09   0.16       0.37  21.6                                        ______________________________________                                    

EXAMPLES 25-28

A master batch of a blend of LCP (Vectra A900 from Hoechst CelaneseCorporation and LCC 10109 from Eastman Kodak Company) in PET at a weightconcentration of 1% was made by dry blending, followed by extrusion withastatic mixer and a 60 micron filter, followed by pelletizing. Afterproper drying the master-batched pellets were then fed by an Acrisonfeeder to anextruder running PET to make cast webs with finalconcentrations as shown in Table 5 below. The cast webs were thenstretched at 99° C. 4×4 times biaxially and heatset at 237° C. intofilms. The coefficients of friction and the RQ were then determined andare reported in Table 5.

                  TABLE 5                                                         ______________________________________                                                LCP                          RQ                                               Vectra/LCC 10109                                                                            Static   Kinetic                                                                             Wheelside                                Example (%)           COF      COF   (nm)                                     ______________________________________                                        25      0.03/0.03     1.06     0.05  8                                        26        0/0.07      3.07     3.25  --                                       27      0.054/0.054   0.43     0.41  11.2                                     28        0/0.7       0.48     0.45  --                                       ______________________________________                                    

Example 26 has relatively high COF values. However, the film has betterCOFvalues than a film with no LCP. Compare Example 26 with Example 21.Additionally, this LCP has a chemical moiety (ethylene terephthalate)which is similar to that of PET. As noted above, this causes its COF tobehigher.

EXAMPLES 29-32

A series of films according to the invention were prepared. CompositionsofLCP (LCC 10108, a copolyester of 60 mole % oxybenzoate and 40 mole %ethylene terephthalate available from Eastman Kodak Company) werepreparedby dry blending the desired quantity of LCP with PET. Afterproper drying, the resulting dry blend was extruded with a static mixerthrough a drop die onto a chilled roll. The cast webs were thenstretched at 99° C. 3.5×3.5 times biaxially and heatset into films. Thecoefficients of friction of the resulting films were then determined andare reported in Table 6 along with the final concentration of LCPemployed.

                  TABLE 6                                                         ______________________________________                                                  LCP          Static  Kinetic                                        Example   (%)          COF     COF                                            ______________________________________                                        29        30           0.44    0.45                                           30        35           0.36    0.36                                           31        40           0.45    0.44                                           32        50           0.42    0.38                                           ______________________________________                                    

EXAMPLES 33-41

A series of dual layer films according to the invention were prepared inwhich the minor layer (approximately 20% of the total film thickness)comprised a combination of LCP (LCC-10108 from Eastman Kodak Company)and PET while the major layer (approximately 80% of the film thickness)comprised pure PET. The LCP-containing material was prepared asdescribed in Example 29 and coextruded with a layer of PET at 260°-290°C. with filters of 100 micron size. The dual layerwas cast from a die at260° C. onto a chilled roll maintained at 91°-94° C. The films ofExamples 33-39 were simultaneously biaxially oriented and the films ofExamples 40 and 41 were sequentially biaxially oriented. They were allstretched at 99° C. to 3.8×3.8 times and heatset at 237° C. Theresulting films weretested for their coefficient of friction by rubbingthe LCP containing sides against each other and by rubbing the LCPcontaining side against the PET side. The concentrations of LCP and thecoefficient of friction results are shown in Table 7.

                  TABLE 7                                                         ______________________________________                                                              Static                                                                              Kinetic                                                                              Static Kinetic                                   LCP     Final   COF   COF    COF    COF                                       Layer   LCP     (LCP/ (LCP/  (LCP/  (LCP/                               Ex.   (%)     (%)     LCP)  LCP)   PET)   PET)                                ______________________________________                                        33     5      1       0.34  0.36   0.42   0.46                                34    10      2       0.35  0.35   0.58   0.54                                35    20      4       0.34  0.34   0.50   0.52                                36    30      6       0.36  0.36   0.51   0.53                                37    40      8       0.38  0.37   0.54   0.53                                38    60      12      0.42  0.37   0.49   0.54                                39    80      16      0.44  0.43   0.57   0.50                                40    30      6       --    --     0.48   0.47                                41    60      12      --    --     0.51   0.53                                ______________________________________                                    

The surface of the films of examples 38-41 comprised large regions orglobules of the LCP in which the host polymer was dispersed.

EXAMPLES 42-45

A series of rough surface films of the invention were made using thetechniques described in Examples 29-32 except using Vectra A900 fromHoechst Celanese Corporation as the LCP. The coefficients of friction ofthe resulting films were then determined and the surface roughnesseswere measured according to the methods set forth in Example 1. Pencilwriteability was tested with a No. 2 pencil. Writeability was gradedgood when it left comparable or darker traces on the film than onordinary paper. The results are reported in Table 8 along with theconcentration ofLCP employed.

                  TABLE 8                                                         ______________________________________                                                                                Pencil                                        LCP      Static   Kinetic                                                                              RQ     Write-                                Example %        COF      COF    (μm)*                                                                             ability                               ______________________________________                                        42       2       0.23     0.23   0.47   fair                                  43       5       0.23     0.21   1.02   good                                  44      10       0.25     0.21   1.01   good                                  45      20       0.30     0.23   1.6    good                                  ______________________________________                                        *Standard deviation of the measurement is 0.18 μm (micrometer)         

The embodiments for which an exclusive property or privilege is claimedare defined as follows:
 1. A method of preparing a film, the methodcomprising the steps of:(a) mixing a thermotropic liquid cyrstallinepolymer with a host polymer to provide a first material; (b) coextrudingthe first material with a second material so as to form a film having atleast two layers wherein the first material forms a first layer and thesecond material forms a second layer; (c) quenching the film; and (d)orienting the quenched film in at least one direction; wherein theoriented film has an exposed first major surface comprising protrusionsresulting from regions of the liquid cyrstalline polymer in the hostpolymer.
 2. A method according to claim 1, the film comprising at leastabout 0.01 weight percent of the liquid crystalline polymer.
 3. A methodaccording to claim 1, wherein the second layer of the film issubstantially free from the liquid crystalline polymer relative to thefirst layer.
 4. A method according to claim 3 wherein the second layeris at least about 80% of the thickness of the film.
 5. A methodaccording to claim 1 wherein the second material comprises substantiallythe same material as the host polymer.
 6. A method according to claim 1wherein the second material is substantially free from liquidcrystalline polymer relative to the first material.
 7. A methodaccording to claim 1 wherein the first layer is at most about 20% of thethickness of the film.
 8. A method according to claim 1 wherein the filmis biaxially oriented.
 9. A method according to claim 1 furthercomprising a step of heat setting the film.
 10. A method according toclaim 1 further comprising a step of applying a layer of a thirdmaterial to the film.
 11. A method according to claim 10 wherein thefilm comprises a second major surface opposite the first major surfaceand further wherein the layer of the third material is applied to thesecond surface.
 12. A method according to claim 11 wherein the thirdmaterial is a magnetic recording media.
 13. A method according to claim11 wherein the third material is a radiation sensitive material.
 14. Amethod according to claim 11 wherein the third material is an abrasive.15. A method according to claim 1 wherein the liquid crystalline polymercomprises at least about 1.0 weight percent of the film.
 16. A methodaccording to claim 1 wherein the film has a coefficient of friction of0.8 or less.
 17. A method according to claim 1 wherein the film furthercomprises a layer of a third material.